As is well known in the art, the human heart has four valves that control blood flow circulating through the human body. On the left side of the heart is the mitral valve, located between the left atrium and the left ventricle, and the aortic valve, located between the left ventricle and the aorta. Both of these valves direct oxygenated blood from the lungs into the aorta for distribution through the body.
The tricuspid valve, located between the right atrium and the right ventricle, and the pulmonary valve, located between the right ventricle and the pulmonary artery, however, are situated on the right side of the heart and direct deoxygenated blood from the body to the lungs.
The peripheral venous system also includes a number of valves that prevent retrograde blood flow. By preventing retrograde blood flow, the valves found throughout the venous system assist the flow of blood through the veins and returning to the heart.
Normally, the mitral valve has two leaflets and the tricuspid valve has at least two, preferably three leaflets. The aortic and pulmonary valves, however, have normally at least two, preferably three leaflets, also often referred to as “cusps” because of their half-moon like appearance.
Venous valves are usually of the bicuspid type, with each cusp or leaflet forming a reservoir for blood, which, under pressure, forces the free edges of the cusps together to permit mostly antegrade blood flow to the heart. As discussed in detail below, since a majority of venous blood flow is against gravity while a person is standing, incompetent or destroyed venous valves can cause significant medical problems in the legs, ankles, and feet.
Valve diseases are typically classified into two major categories; stenosis and insufficiency. In the case of a stenosis, the native valve does not open properly, whereby insufficiency represents the opposite effect showing, deficient closing properties.
Insufficiency of the inlet (atrioventricular) tricuspid valve to the right ventricle of the heart results in regurgitation of blood back into the right atrium, which, serving to receive blood flow returning in the veins from the entire body, then results in turn in suffusion and swelling (edema) of all the organs, most notably in the abdomen and extremities, insufficient forward conduction of blood flow from the right ventricle into the lungs causing compromise of pulmonary function, and ultimately pump failure of the right heart. Collectively, these conditions are termed right heart failure; a condition that leads to incapacity and possibly to death if progressive and uncorrected.
Insufficiency of vein function due to the incompetence or destruction of peripheral venous valves leads to acute then chronic swelling of the veins and their dependent lymphatics and tissues. This condition can affect the deep veins of the body, commonly the lower extremities or pelvis, or the superficial veins of the lower extremities in particular, leading to progressive expansion of the veins and further valvular incompetence, a condition known as varicose veins.
Medical conditions like high blood pressure, inflammatory and infectious processes often lead to stenosis and insufficiency. Treatment of heart valve dysfunctions typically include reparation of the diseased heart valve with preservation of the patient's own valve or replacement of the valve with a mechanical or bioprosthetic valve (i.e. “tissue” valve), i.e. a prosthetic valve. Particularly for aortic heart valves, however, it is frequently necessary to introduce a heart valve replacement.
Various prosthetic heart valves have thus been developed for replacement of natural diseased or defective valves. Illustrative are the one-piece bioprosthetic “tissue” valves disclosed in Applicant's Co-Pending application Ser. No. 13/560,573.
A major drawback associated with most one-piece prosthetic valves is that the valves are typically sized and configured for replacement of a defined valve, i.e. aortic, pulmonary, mitral, tricuspid or peripheral venous valve. A sizable number of one-piece prosthetic valves must thus be produced to accommodate replacement of diseased or defective aortic, pulmonary, mitral, tricuspid or peripheral venous valves.
The implantation of a prosthetic valve, including mechanical valves and bioprosthetic valves, also requires a great deal of skill and concentration given the delicate nature of the native cardiovascular tissue and the spatial constraints of the surgical field. It is also critical to achieve a secure and reliable attachment of the valve to host cardiovascular tissue.
Various structures and means have thus been developed to provide a secure and reliable attachment of a prosthetic valve to host cardiovascular tissue. Most surgical techniques comprise suturing the ends of the valve to the annulus of the cardiovascular vessel.
There are numerous drawbacks and disadvantages associated with suturing a valve to host tissue. A major disadvantage is the high risk of perivalvular leakage.
In application Ser. No. 13/560,573, the tissue valve includes a sewing ring that can be employed to suture the ends of the valve to the annulus of the cardiovascular vessel. Although the use of a sewing ring to secure the valve to a cardiovascular vessel can be, and most times is, highly effective, success of the technique is still highly dependent on the skill of the surgeon.
There is thus a need to provide prosthetic valves that can be readily employed to selectively replace diseased or defective aortic, pulmonary, mitral, tricuspid and peripheral venous valves.
There is also a need to provide prosthetic valves having means for secure, reliable and consistent attachment to cardiovascular vessels.
It is therefore an object of the present invention to provide two-piece prosthetic tissue valves that can be readily employed to selectively replace diseased or defective aortic, pulmonary, mitral, tricuspid and peripheral venous valves.
It is another object of the present invention to provide two-piece prosthetic tissue valves having means for secure, reliable, and consistently highly effective attachment to cardiovascular vessels.
It is another object of the present invention to provide two-piece prosthetic tissue valves that substantially reduce or eliminate intimal hyperplasia after intervention in a vessel and the harsh biological responses associated with conventional polymeric and metal valves.